It has been found that many types of nettings, exposed to sea and lake waters, experience heavy levels of clogging due to algae and invertebrates. Such clogging limits the flow of water and deposited organisms in the enclosed area with concomitant weight increases as high as 1000 percent. Such a weight increase results in the sinking of the supported netting and fish escape as well as making it practically impossible to raise the netting for cleaning. In some instances, the cutting away of netting is necessitated resulting in the loss of netting. In addition to netting losses, fish may also be lost or harmed. Salt and freshwater aquaculture systems have traditionally been plagued by heavy fouling on nets, cages, intake pipes and aeration systems. Nets particularly have suffered from heavy incrustation making them inordinately heavy, and eventually incapable of permitting water, flow-through. Natural food penetration, acceptable oxygen levels and detritus removal are severely restricted, leading to poor crop yield. Labor for frequent cleaning adds high costs and full cage utilization is not possible because of cage rotation during cleaning. Antifouling compounds have been used for centuries with only partial success. Traditional anti-fouling coating treatments have relied on copper and mercury compounds which are effective anti-foulants but are highly toxic and can be damaging to systems in which live organisms are expected to survive.
In the hereinabove mentioned co-pending applications, there is disclosed a net finishing composition in a suitable solvent system which when coated on a net substrate, particularly a nylon net substrate of a mesh size of from 1/4 to 24 inches, substantially improves the integrity of the net substrate concommitantly improving seining qualities in terms of improved daily catch. The net fishing composition is comprised of a low molecular weight, high acetate content, vinyl chloride copolymer, a monomeric plasticizer and a polymeric plasticizer. The molecular weight of the copolymer is from 20,000 to 65,000 and of an acetate content of from 10-20 percent by weight. The plasticizers are present in an amount of from 40 to 60 parts, preferably 50 parts per 100 parts of the copolymer with the ratio on monomeric plasticizer to polymeric plasticizer ranging from about 1:1 to 3:1, preferably 2:1. It is also disclosed that antifouling properties could be improved by adding certain organo tin esters dissolved or dispersed in the solvent system.
In U.S. Pat. No. 4,010,141 to Onozuka et al. there is disclosed a plurality of tin compounds, and in particular dimethyl, n-alkyl tin esters of improved antifouling characteristics. While such trialkyl tin esters have shown some efficacy, such trialkyl tin esters are compatible with the plasticizers in the resin and can readily leach out or can be locked into the film after application to a netting substrate.